The present invention relates to new herbicidal compositions comprising a glyphosate type herbicide and a phenoxybenzoic type herbicide. It also relates to methods for the treatment of undesirable plants using these compositions.
Glyphosate (i.e. N-phosphonomethylglycine) and its salts are well known wide spectrum herbicides which are active against annual and perennial weeds. This class of herbicides is well known for its post-emergence efficacy and is used for agricultural and garden applications. Nevertheless, it is still desirable to improve the herbicidal activity of these compounds.
It is known that glyphosate type herbicides act relatively slowly. In fact, a period of approximately three weeks is generally required before the effects are observed.
In order to overcome this disadvantage, PCT Patent Application WO 84/03,607 indicates that in the specific case of application to amateur gardens, the addition of a certain quantity of acifluorfen or one of its salts to glyphosate type herbicides increases the speed of action of such herbicides. In this context, an herbicidally effective quantity of glyphosate type herbicide is employed and acifluorfen is added so that the ratio by weight of glyphosate to acifluorfen is in practice between 1:8.33 and 4.2. However, it is observed that the compositions described reveal a marked antagonism in many cases, which results in the efficacy of the glyphosate type herbicide being adversely affected. The use of extemporaneous mixtures of glyphosate and acifluorfen against weeds of field crops such as soybeans, and not of garden weeds, has also been proposed. Thus, the publication: Proceedings, Southern Weed Science Society, 38th annual meeting, Sandberg et al., 1985, pages 86-89, indicates that 430 g/ha of glyphosate combined with 70 g/ha of acifluorfen shows a marked antagonism against the weeds tested. This antagonism decreases, however, when the glyphosate:acifluorfen ratio decreases, i.e. when the quantity of acifluorfen is increased.
A second publication, Ibid, pages 64-67, Frost, also confirms the fact that it is necessary to increase the dose of acifluorfen.
It is also seen from the latter publication that the spectrum of activity of glyphosate is reduced, especially against graminaceous plants.
Another disadvantage related to the mode of action of glyphosate or its derivatives lies in the fact that it can very easily be washed out, i.e. if there is heavy rainfall within a few hours of its application, a large part of it is removed. It is also desirable to improve the action of glyphosate type herbicides on plants whose growth is slowed down by low temperatures and/or low humidity, or on plants which are at the end of their growth cycle.
In an unexpected way, the present invention enables these disadvantages to be overcome and more particularly, enables one or more of the following advantages to be achieved:
1. increase in the speed of action of glyphosate type herbicides; PA0 2. improvement in the activity spectrum of glyphosate type herbicides; PA0 3. improvement in the herbicidal properties of glyphosate type herbicides; PA0 4. prevention of glyphosate type herbicides from being washed out; and PA0 5. improvement in the activity of glyphosate type herbicides on plants whose growth is slowed down by low temperatures and/or low humidity or on plants which are at the end of their growth cycle.